<!doctype html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport"
          content="width=device-width, user-scalable=no, initial-scale=1.0, maximum-scale=1.0, minimum-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
    <style>
         *{
             margin: 0;
             padding: 0;
         }
        body {
  /*  background: url('http://csssecrets.io/images/stone-art.jpg');*/
      background: red
}

.border1 {
    border: 10px solid hsla(0,0%,100%,.5);
    background: white;
    background-clip: padding-box;
    
    /* styling */
    max-width: 20em;
    padding: 2em;
    margin: 2em auto 0;
    font: 100%/1.5 sans-serif;
}
    </style>
</head>
<body>
     <h1>半透明边框</h1>
      <div class="border1">半透明</div>
</body>
</html>
